PTL 1 discloses the use of an azo pigment as a toner colorant. In order to improve spectral characteristics, such as tinting strength and transparency, a pigment must be finely dispersed in a toner binder resin or a polymerizable monomer. However, a reduction in the size of azo pigment particles generally results in an increase in the growth or transformation of crystals caused by thermal history or contact with a solvent in a dispersion process and subsequent processes. This results in a decrease in the tinting strength and transparency of the toner. Furthermore, in a toner manufacturing process using an azo pigment, particularly utilizing a polymerization method, the reaggregation of fine azo pigment particles may cause an increase in the viscosity of the pigment dispersion.
Various pigment dispersants have been proposed in order to solve these problems. PTL 2 discloses a polymer dispersant in which a moiety having a high affinity for an azo pigment colorant is covalently bonded to an oligomer or polymer moiety having a high affinity for a solvent and a binder resin. PTL 3 discloses the use of a comb polymer dispersant having an acidic or basic portion known as Solsperse (registered trademark).